Terpyridine based ReX(CO)₃ compounds (X = Br^–, N₃^– and triazolate): Spectroscopic and DFT studies

[ReX(CO)₃(L–k²N¹,N²)] (L = 4′-(4-phenyl morpholine)-2,2′:6′,2′'-terpyridine, X = Br^– (1), N₃^– (2), and triazolate (3)) complexes were synthesized, and characterized using different spectroscopic and analytical tools including single-crystal X-ray diffraction analysis of 2. The 1,3-dipolar cycloaddition reaction between 2, and 4,4,4-trifluoro-2-butynoic acid ethyl ester afforded triazolate 3. Although, the crystal structure of 2 showed that the azide ligand is terminally coordinated to Re(CO)₃⁺ unit, the ¹⁹F and ¹H NMR analyses of 3 provided conversant evidences that the kinetically formed N(1) triazolate bound isomer favoured the isomerization to N(2) form. The photophysical properties of 1–3 were investigated by recording the absorption spectra of the compounds in solvents of different polarities. Complexes 1 and 3 were screened for their potential antimicrobial activities. The protein binding affinity of 1, and 3 towards hen white egg lysozyme revealed that the bromide complex exchanges Br^– with that protein, while the triazolate analogue sticked around.